Part C - The replication bubble and antiparallel elongation
DNA replication always begins at an origin of replication. In bacteria, there is a single origin of replication on the circular chromosome, as shown in the image here. Beginning at the origin of replication, the two parental strands (dark blue) separate, forming a replication bubble. At each end of the replication bubble is a replication fork where the parental strands are unwound and new daughter strands (light blue) are synthesized. Movement of the replication forks away from the origin expands the replication bubble until two identical chromosomes are ultimately produced.
Diagram showing DNA replication in a circular chromosome. For simplicity, the double-stranded DNA is shown as two concentric circles. There is one origin of replication, where the two parental strands (shown in dark blue) separate, forming a replication bubble. At each end of the replication bubble is a replication fork (indicated by a pink arrow) where the parental strands are unwound and new daughter strands (shown in light blue) are synthesized. The replication forks move away from the origin and expand the replication bubble. As the light blue strands elongate, the two double-stranded circles that are forming start to peel off from each other. The end result is two separate, identical daughter DNA molecules, each composed of one parental strand (dark blue) and one new strand (light blue).
In this activity, you will demonstrate your understanding of antiparallel elongation at the replication forks. Keep in mind that the two strands in a double helix are oriented in opposite directions, that is, they are antiparallel.
Drag the arrows onto the diagram below to indicate the direction that DNA polymerase III moves along the parental (template) DNA strands at each of the two replication forks. Arrows can be used once, more than once, or not at all.
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